A top view (top) and side view (bottom) of the cobalt-boron molecular drum, CoB16–. The connections between atoms help visualize the structure but do not necessarily indicate bonds.

Credit: Alexander Boldyrev

A top view (top) and side view (bottom) of the cobalt-boron molecular drum, CoB16–. The connections between atoms help visualize the structure but do not necessarily indicate bonds.

Credit: Alexander Boldyrev

A multinational research team has created a drum-shaped cobalt-boron species in the gas phase, CoB16–, which sets a record for highest coordination number in a molecule. The sandwich complex created by Alexander I. Boldyrev of Utah State University, Lai-Sheng Wang of Brown University, and their colleagues consists of two B8 rings connected to the central cobalt atom via 16 bonds, the theoretical maximum based on the number of available atomic orbitals. Boron is particularly useful in such efforts because the electron-deficient element tends to share electron pairs with multiple other atoms to form strongly bonded network structures. The researchers made CoB16– by pressing cobalt and boron into a pellet and then vaporizing it with a laser beam. They used a mass spectrometer to select CoB16– clusters from the product mixture and analyzed them with photoelectron spectroscopy. The team correlated the experimental results with computational analysis (Nat. Commun. 2015, DOI: 10.1038/ncomms9654). The previous record stood with a 15-coordinate thorium complex, Th[(H3B)2N(CH3)2]4, which remains the most-coordinated molecule that has been isolated in a condensed state. Boldyrev and Wang believe their work on CoB16– could inspire synthetic chemists to find a way to produce isolable clusters for use as nanomaterial building blocks.